<meta charset="utf-8">
(#) Using Modifier.then with a Modifier factory function with an implicit receiver

!!! ERROR: Using Modifier.then with a Modifier factory function with an implicit receiver
   This is an error.

Id
:   `SuspiciousModifierThen`
Summary
:   Using Modifier.then with a Modifier factory function with an implicit receiver
Severity
:   Error
Category
:   Correctness
Platform
:   Any
Vendor
:   Jetpack Compose
Identifier
:   androidx.compose.ui
Feedback
:   https://issuetracker.google.com/issues/new?component=612128
Min
:   Lint 8.0 and 8.1
Compiled
:   Lint 8.0 and 8.1
Artifact
:   [androidx.compose.ui:ui-android](androidx_compose_ui_ui-android.md.html)
Since
:   1.7.0
Affects
:   Kotlin and Java files and test sources
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/ui/ui-lint/src/main/java/androidx/compose/ui/lint/SuspiciousModifierThenDetector.kt)
Tests
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/ui/ui-lint/src/test/java/androidx/compose/ui/lint/SuspiciousModifierThenDetectorTest.kt)
Copyright Year
:   2024

Calling a Modifier factory function with an implicit receiver inside
Modifier.then will result in the receiver (`this`) being added twice to
the chain. For example, fun Modifier.myModifier() =
this.then(otherModifier()) - the implementation of factory functions
such as Modifier.otherModifier() will internally call this.then(...) to
chain the provided modifier with their implementation. When you expand
this.then(otherModifier()), it becomes:
this.then(this.then(OtherModifierImplementation)) - so you can see that
`this` is included twice in the chain, which results in modifiers such
as padding being applied twice, for example. Instead, you should either
remove the then() and directly chain the factory function on the
receiver, this.otherModifier(), or add the empty Modifier as the
receiver for the factory, such as this.then(Modifier.otherModifier())

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/TestModifier.kt:10:Error: Using Modifier.then with a Modifier
factory function with an implicit receiver [SuspiciousModifierThen]
    fun Modifier.test2() = this.then(test())
                                     ----
src/test/TestModifier.kt:12:Error: Using Modifier.then with a Modifier
factory function with an implicit receiver [SuspiciousModifierThen]
    fun Modifier.test3() = this.then(with(1) { test() })
                                               ----
src/test/TestModifier.kt:14:Error: Using Modifier.then with a Modifier
factory function with an implicit receiver [SuspiciousModifierThen]
    fun Modifier.test4() = this.then(if (true) test() else TestModifier)
                                               ----
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test/TestModifier.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package test

import androidx.compose.ui.Modifier

object TestModifier : Modifier.Element

fun Modifier.test(): Modifier = this.then(TestModifier)

fun Modifier.test2() = this.then(test())

fun Modifier.test3() = this.then(with(1) { test() })

fun Modifier.test4() = this.then(if (true) test() else TestModifier)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/ui/ui-lint/src/test/java/androidx/compose/ui/lint/SuspiciousModifierThenDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `SuspiciousModifierThenDetector.errors`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=612128.

(##) Including

!!!
   This is not a built-in check. To include it, add the below dependency
   to your project.

```
// build.gradle.kts
implementation("androidx.compose.ui:ui-android:1.8.0-alpha07")

// build.gradle
implementation 'androidx.compose.ui:ui-android:1.8.0-alpha07'

// build.gradle.kts with version catalogs:
implementation(libs.ui.android)

# libs.versions.toml
[versions]
ui-android = "1.8.0-alpha07"
[libraries]
# For clarity and text wrapping purposes the following declaration is
# shown split up across lines, but in TOML it needs to be on a single
# line (see https://github.com/toml-lang/toml/issues/516) so adjust
# when pasting into libs.versions.toml:
ui-android = {
    module = "androidx.compose.ui:ui-android",
    version.ref = "ui-android"
}
```

1.8.0-alpha07 is the version this documentation was generated from;
there may be newer versions available.

NOTE: These lint checks are **also** made available separate from the main library.
You can also use `androidx.compose.ui:ui-lint:1.8.0-alpha07`.


[Additional details about androidx.compose.ui:ui-android](androidx_compose_ui_ui-android.md.html).
(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("SuspiciousModifierThen")
  fun method() {
     then(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("SuspiciousModifierThen")
  void method() {
     then(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection SuspiciousModifierThen
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="SuspiciousModifierThen" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'SuspiciousModifierThen'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore SuspiciousModifierThen ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

<!-- Markdeep: --><style class="fallback">body{visibility:hidden;white-space:pre;font-family:monospace}</style><script src="markdeep.min.js" charset="utf-8"></script><script src="https://morgan3d.github.io/markdeep/latest/markdeep.min.js" charset="utf-8"></script><script>window.alreadyProcessedMarkdeep||(document.body.style.visibility="visible")</script>